Barrier fabrics are generically characterized as being impervious to penetration by liquids. Barrier fabrics with much more stringent technical requirements, are also especially suited for use in the medical field to prevent or control the spread of infectious microorganisms, such as viruses and bacteria, blood, and other fluid transmissions associated with, for example, surgical procedures.
Barrier fabric properties are critical for medical products such as surgical drapes that are used to maintain sterile surgical and/or procedure fields and protective apparel such as surgical gowns. These barrier fabrics are widely used in hospitals, doctor's offices, clinics, and the like by health professionals such as doctors, medical assistants, nurses, and nurses' aides. Particularly where there is a possibility of coming into contact with contaminated body fluids, every effort is made to protect the health professional and the patient. Health professionals routinely use medical barrier fabrics during surgery, the drawing of blood, or while working with specimens containing contaminated fluids to both protect themselves and to avoid cross or secondary contamination of subsequent patients through the inadvertent transmission of infectious materials.
There are currently two types of medical barrier fabrics: single use, i.e., disposable materials and reusable materials. Disposable fabrics are typically constructed from non-wovens made from light-weight synthetic fibers or synthetic fibers blended with natural fibers. Performance of the disposable non-woven fabrics in terms of liquid repellency is generally acceptable; however, these fabrics often fail to provide the spectrum of properties deemed necessary to achieve desirable protection in many medical applications.
Reusable medical barrier fabrics, on the other hand, are usually woven and constructed from cotton, cotton/polyester blends, or polyester and have a high thread count to provide a physical barrier to prevent or reduce the spread of infectious materials or vectors. While reusable woven fabrics per se offer more comfort in terms of drapeability and hand and the potential for lower cost per use, they lack the liquid repellency the market has come to expect on the basis of experience with the disposables, and usually lose some of their protective properties over time, especially after repeated launderings and steam (autoclave) sterilizations.
Acquisition costs and the number of times a product manufactured with a protective barrier fabric such as a surgical gown can be reused, have a direct bearing on the per use cost of the product. With respect to disposable surgical gowns for instance, the per use cost is, in essence, simply their acquisition cost and the cost of disposal. Disposable gowns certainly have an advantage in convenience. However, reusable gowns have a tactile advantage in that they have a nice drapeability and feel, which is preferred over that of the disposable gowns that are fabricated of non-woven fabrics. Drapeability and feel are important factors of the “hand” of the textile fabrics employed in constructing reusable surgical gowns.
All of this is to emphasize that there is a competitive motivation to minimize the per use cost of reusable medical/surgical barrier protective apparel and products.
Importantly however, reusable surgical gowns, surgical drapes, and other non-disposable medical/surgical barrier fabric products have further requirements which distinguish them from other products or garments that incorporate barrier fabrics. To wit, after each use, a reusable surgical gown, for example, must be washed, dried and sterilized for subsequent reuse. These procedures involve harsh detergents and high temperatures which can quickly degrade the barrier properties of the gown and limit the number of times the gown can be reused.
A typical, institutional laundering/autoclaving cycle for such reusable medical/surgical products generally comprises an initial flush in which the products are soaked in water at 90°-100° F. for two to five minutes. The products are then soaked in an alkali (a pH in excess of 10) bath at 120°-150° F. for three to ten minutes to loosen dirt. Next the products are placed in a detergent bath at approximately 160° F. for approximately six to ten minutes. Next is a bleach bath at approximately 150° F. for approximately six minutes. This is followed by one or more rinsings at temperatures which may be progressively reduced from 160° F. to ambient temperature. Finally, there is an acid sour bath in which the pH is adjusted to the four to seven range, and in which a softening agent may also be employed. There is then one or more rinse baths.
The products are mechanically agitated in some, if not all of these baths. Also, following each bath, there is an extraction (spin) cycle to minimize the liquid carried over to the succeeding process.
The products are then dried in a tumbling dryer at an average temperature of 160° F. Typical drying times for products are in the order of 20 to 40 minutes. It is to be noted that there can be hot spots in such dryers, which can subject the products to temperatures in excess of 400° F.
After drying, the products are placed in an autoclave and sterilized by pressurized steam at a temperature of approximately 260° F. for at least four, and preferably about fifteen minutes.
These harsh conditions are several orders of magnitude greater than those existing in the laundering or dry cleaning of barrier fabrics incorporated in ordinary garments. In fact, many of the barrier fabrics intended for use in normal garments, such as foul weather gear, become unusable after a single, or relatively few, institutional laundering/autoclaving cycles.
Polymeric films have traditionally been used as a laminate with textile fabrics to provide barrier properties for limited use medical products such as surgical drapes and gowns constructed of disposable fabric and the art is replete with references to these laminates and medical uses thereof (e.g., U.S. Pat. Nos. 4,379,192 and 6,238,767). Microporous films and methods for making such films are taught, for example, by U.S. Pat. No. 3,844,865 and laminates employing such porous films and non-woven materials are taught, for example, in U.S. Pat. Nos. 5,560,974; 5,169,712; 6,610,163; and 5,695,868.
Typically the fabric utilized in the disposable composites is a non-woven material and the films include low basis weight polyethylenes, polypropylenes, blends including polyolefins and copolymers such as ethylene and propylene copolymers. When repeated institutional washing and sterilization cycles are attempted with these composites, these laminated film products quickly delaminate and are unable to retain many of their necessary protective barrier properties. Procedures to prevent the undesirable delamination of the barrier protective fabric during and/or after multiple wash/sterilization cycles have taken many forms: primarily by using polymer coating, impregnating or saturating techniques, and/or using these techniques with multiple layering of woven fabric, polymer, and/or polymer treated woven fabric. Maximum functionality has been achieved with these techniques by the art via the use of fluorochemical and silicone type polymers.
Early silicone woven fabric coatings tended to degrade the tactile finish or hand of the fabric and give the coated fabric side a rubberized finish which was not appealing for many fabric uses, particularly garments. The art has also struggled with coated applications of the polyorganosiloxanes in attempting to achieve high levels of resistance to liquid. Although the art has coated porous textile webs with silicone, these early silicone polymers tended to remain on the surface of the fabric, i.e., the polymer did not provide a film over the individual internal fibers and/or yarn bundles. As a result, the coatings tended to abraid and/or wash away quickly.
To get the polymer to penetrate deeper into the interstices of the fabric, saturation or impregnation techniques are used by the art. These techniques are typically accomplished by immersion of the fabric using a low viscosity, liquid silicone resin. In this manner, the low viscosity polymer fluid can flow readily into the web interstices and be adsorbed or absorbed therewithin. This immersion application of a liquid or paste composition to a fabric can be achieved, for example, by the so-called padding process wherein a fabric material is passed first through a bath and subsequently through squeeze rollers in a process sometimes called single-dip or single-dip padding. Alternatively, the fabric can be passed between squeeze rollers, the bottom one of which carries the liquid or paste composition in a process sometimes called double-dip or double-dip padding. This process however, as taught in U.S. Pat. No. 2,673,823, tends to produce a heavily silicone impregnated, rubberized material, i.e., the interstices of the fabric are usually completely filled or saturated. Such a treated web is substantially devoid of its original tactile and visual properties and instead has the characteristic rubbery properties of a cured silicone polymer.
Prior treatments of webs that force a composition into the spaces of the web have relied, to aid in the flow of the composition as taught in U.S. Pat. No. 3,594,213, on using low viscosity compositions with solvents such as water or volatile organic based solvents. However, such solvent based systems tend to deposit the polymer on the fabric in a random and inconsistent manner, creating individual spots of polymer thus limiting the overall adhesive strength of the resultant product. And, of course, solvent processing often has environmental and economic consequences relating to the removal and disposal of the solvent. Use of a non-curable solvent and heat are disclosed to reduce the viscosity of a polymeric composition for porous fabric saturation in U.S. Pat. No. 4,588,614.
Another method that has fairly successfully achieved a fabric with high liquid impermeability properties after multiple institutional launderings/autoclavings and is one of the current commercially acceptable technologies of choice, is that set forth in U.S. Pat. Nos. 5,236,532 and 5,183,702 wherein a thin film of uncured silicone in a highly viscous state is compressed between a pair of rolls onto a tightly woven fabric which had been formed with “nubs” on the contact surface and previously treated with a hydrophilic finish. The composite is subsequently cured.
Many references disclose the use of layering techniques in attempts to maximize the desirable properties of barrier fabrics. Such techniques include laminating treated fabrics, untreated fabrics, and/or porous film with an adhesive tie coat; however, these techniques exhibit the same limitations described above for solid film, laminated fabric products, e.g., delamination during abrasion or washing/sterilization cycles and, in addition, suffer from the environmental issues that arise vis-a-vis the adhesive usage. Furthermore, additional difficulties can be encountered in ensuring that the mechanical performance differential between the various layers such as the treated substrate, the adhesive, the film, etc. is balanced. For example, if shrinkage of any of the three materials mentioned above, passes the initial yield stress of either of the other materials, there will be deformation; and, if it passes the ultimate tensile strength, there will be delamination of the multilayered composite.
U.S. Pat. Nos. 4,872,220; 5,024,594; 5,180,585; 5,335,372; 5,391,423; 5,532,053; and 6,238,767 describe products that use layers of fabrics and/or polymers to prevent blood, microbes, and viruses from penetration through the fabric composites. Additionally, U.S. Pat. No. 4,991,232 describes a medical garment comprising a plurality of plies to prevent blood from penetrating through the garment. Similarly, U.S. Pat. No. 5,027,438 creates a barrier composite material by sandwiching a bacteriostatic impregnated fabric between two microporous urethane coated fabrics. Detrimentally, this layering of fabrics and/or polymers traditionally results in heavier garments and utilizes additional raw materials.
Another technique utilized in the art for realizing a low viscosity fluid polymer and using same to penetrate the interstices of a fabric is through the use of a thixotropic or pseudoplastic polymer which is applied to a fabric substrate while the polymer is under high shear. This process and products made therefrom are currently one of the technologies of choice in the commercial, medical barrier fabric arena. U.S. Pat. No. 6,071,602 discloses such a technique for controlling the bond adhesion and the effective porosity of a web and thus realizing a web that is said to be resistant to permeation by a disease causing microorganism. U.S. Pat. Nos. 6,342,280 and 6,416,613 also use the thixotropic methodology to produce a multilayered composite material which comprises shear thinning an uncured, essentially solvent free, pseudoplastic polymer; applying this liquid onto a porous substrate thereby encapsulating most of the fibers while leaving some interstitial spaces open; applying a layer of polymer to a surface of the uncured, encapsulated substrate; pressuring the layer into the uncured encapsulated substrate; and curing the completed composite. Polymers that can be successfully used in this process are said to include silicones, polyurethanes, fluorosilicones, acrylics, polytetrafluoroethylene (PTFE), neoprenes, and mixtures thereof.
An important technology in the protective barrier fabric art is that which utilizes expanded, microporous polytetrafluoroethylene (ePTFE) film. Disclosures relating to these ePTFE films usually depict them as being part of a three layer composite. For example, U.S. Pat. No. 4,433,026 teaches a barrier fabric wherein the ePTFE film is sandwiched between a woven polyester fabric and a knitted polyester fabric; U.S. Pat. No. 5,155,867 discloses a barrier fabric undergarment wherein the ePTFE film is layered upon a hydrophilic polyurethane membrane—stretchable knit fabric composite; and U.S. Pat. No. 5,948,707 discloses non-slip cast liners wherein the ePTFE film has a discontinuous coating of an elastomer such as silicone, polyurethane and the like on one side of the film and a soft fabric adhered to the other side of the film.
While the expanded, microporous PTFE protective fabric composites are reported to retain good water repellency, and other barrier properties even after multiple laundering/autoclaving cycles, they tend to be expensive products to manufacture.
In the search for a relatively low cost material that is highly coatable into thin films on fabric substrates without the use of a solvent or expensive apparatus such as high shear generating equipment or high pressure rollers, the art, especially the art relating to the manufacture of air bags, has recently recognized the desirability of using so-called cold curing silicone compositions, in particular, those of the two component type that cross link by hydrosilation or polyaddition in order to produce a thin film elastomer. In general, the two composition parts are mixed together to form a low viscosity composition; coated on a fabric using any conventional process such as a doctor blade or knife over roll, knife over air, transfer or kiss coating, or screen printing process; and heat cured which proceeds by the polyaddition of unsaturated groups (alkenyl, e.g., vinyl-silicon groups) of one polyorganosiloxane onto hydrogens of the same or of another polyorganosiloxane. This is a highly desirable process because these thin film silicone coatings can be applied rapidly and cure quickly upon heating at relatively low temperatures to form coatings that have water repellency which is an inherent characteristic of these silicones. In addition, these coatings have excellent aging behavior, that is, they retain their properties such as their thermal and mechanical properties well over time.
Typical of these two part, cold cure siloxane systems is the composition disclosed in EP-A-0,553,840 containing:                (A) a polydiorganosiloxane having at least two alkenyl groups per molecule,        (B) a polyorganohydrogenosiloxane having at least two hydrogen atoms linked to the silicon in each molecule,        (C) a metal catalyst, the metal being of the platinum group,        (D) an adhesion promoter consisting of an epoxy-functional organosilicon compound,        (E) an inorganic filler, e.g., reinforcing fillers such as fumed titanium oxide, microparticulate silica, e.g., fumed silica, precipitated silica, pyrogenic silica and essentially non-reinforcing fillers, such as quartz powder, diatomaceous earths, iron oxides, aluminum oxides, calcium carbonate or magnesium carbonate; for example, a silica treated by an organosilane, an organosilazane, or a diorganocyclopolysiloxane is incorporated,        (F) a polyorganosiloxane resin, and        (G) optionally a compound used as a crosslinking inhibitor.        
In U.S. Pat. No. 5,296,298, the aforementioned constituents (A) to (E) are again found but the adhesion promoter (D) consists of the combination of an epoxy-functional organosilicon compound with an alkoxylated silane containing, per molecule, a (meth)acryl or (meth)acryloxy group and, optionally, an aluminum chelate, while the inorganic filler (E) is given as being optional, although it is used in all the examples illustrating the invention. As examples of fillers, this document mentions fumed silica, precipitated silica, powdered quartz, diatomaceous earths, and glass beads.
It has been reported that the above-described compositions produced coatings that did not adhere sufficiently well to synthetic nylon fabric to be satisfactorily applied to air bag end-usage.
EP-A-0,681,014 discloses a two part, cold cure siloxane composition similar to the above which yields a coating with significantly improved fabric adhesion properties. The silicone coating composition described consists of a mixture formed by:                (I) at least one polyorganosiloxane having, per molecule, at least two C2-C6 alkenyl groups linked to the silicon,        (II) at least one polyorganosiloxane having, per molecule, at least two hydrogen atoms linked to the silicon,        (III) a catalytically effective amount of at least one catalyst, composed of at least one metal belonging to the platinum group,        (IV) an adhesion promoter,        (V) optionally a mineral filler,        (VI) optionally at least one crosslinking inhibitor, and        (VII) optionally at least one polyorganosiloxane resin,in which the adhesion promoter consists exclusively of the at least ternary combination of the following ingredients:        (IV.1) at least one alkoxylated organosilane containing, per molecule, at least one C2-C6 alkenyl group,        (IV.2) at least one organosilicon compound which includes at least one epoxy radical, and        (IV.3) at least one metal M chelate and/or one metal alkoxide of the general formula: M(OJ)n, with n=the valency of M and J=a linear or branched C1-C8 alkyl, M being selected from the group consisting of: Ti, Zr, Ge, Li, Mn, Fe, Al, and Mg.        
A reinforcing filler such as a pyrogenic silica appears in all of the examples of this teaching.
For reasons of economic competitiveness in the air bag fabric industry, it is highly desirable to be able to apply very thin layers of silicone, i.e., the add-on weight of the coating on the fabric should be less than 30 g/m2.
To that end, U.S. Pat. No. 6,586,551 modified the '014 composition by eliminating all reinforcing filler from the composition. In this manner, it is reported that low add-on weight, coated fabrics, especially polyamide fabrics for the air bag industry, are able to be easily obtained without having a negative impact on the properties that had been realized with the filled compositions such as fire and temperature resistance, creasing and abrasion resistance, and thermal insulation; all of which were actually improved by the removal of the filler.
With a diametrically opposite approach, U.S. Pat. No. 6,562,737, in order to allow coating thickness on a substrate to be increased without increasing the weight of the coated substrate while still retaining acceptable (air bag) end use properties such as thermal resistance properties, added expandable, organic microspheres having a polymer wall to the coating composition; said spheres containing a liquid or a gas. The spheres are preferably incorporated into the coating composition before their expansion, which may then be induced by suitable heating during crosslinking of the elastomer coating.
While the efforts to prepare thinly coated barrier fabrics with required liquid and microorganism repellency have generally been acceptable, economic cost effectiveness is still an elusive target because adhesive and/or polymer bonding failures under severe usage, e.g., heavy abrasion, numerous foldings, and/or multiple harsh institutional type washing/sterilization cycles result in random delaminations, pin-holes, and breakdowns in the protective properties of the barrier fabric, which significantly shorten the potential useful life of the barrier fabric.
Accordingly, it is an object of the instant invention to realize a protective barrier fabric composite, especially a polyester containing one suitable for the medical barrier fabric market, which has excellent initial viral and liquid repellency properties and which is able to sustain those properties after at least 75 institutional laundering/autoclaving cycles and to provide a process for producing same.